Although there is compelling evidence that the [unreadable]-amyloid peptide (A[unreadable]) is centrally involved in Alzheimer's disease pathology, the mechanisms of A[unreadable] toxicity and its specific targets remain unresolved. This project is a continuation of our studies using the intensely studied nematode worm Caenorhabditis elegans as a model to investigate the basis of (human) A[unreadable] toxicity. We have previously shown that transgenic worms engineered to express human A[unreadable] 1-42, replicate some aspects of Alzheimer's disease pathology. By a combination of molecular and genetic approaches, we have now identified a set of conserved genes that modulate A[unreadable] toxicity in these transgenic worm models. In addition, analysis of transgenic worms expressing single amino acid variants has led to the identification of an A[unreadable] variant that is substantially non-toxic in vivo. The goal of this proposal is to synthesize these findings to establish: 1) the identity of the toxic A[unreadable] species, 2) the cellular pathways that influence the formation of the toxic species, and 3) the specific cellular targets of A[unreadable]. The Specific Aims of this proposal are to: 1) perform an in vivo structure/function analysis of A[unreadable] toxicity by constructing and characterizing transgenic worms expressing variant A[unreadable] peptides. These studies will directly test the "toxic A[unreadable] oligomer" model, 2) determine the molecular mechanisms by which evolutionarily conserved modifier genes alter A[unreadable] toxicity, and 3) validate the proposed mechanisms for both A[unreadable] toxicity and the protective genes we have identified using mammalian cell culture and primary neuronal cultures. Our proposed studies have direct relevance for the diagnosis and treatment of Alzheimer's disease. The identity of the key toxic form(s) of A[unreadable] may be critical for designing drugs that prevent its formation or toxic activity. Characterization of genes that affect the toxicity of A[unreadable] may be important for both risk assessment and the development of effective interventions for Alzheimer's and other neurodegenerative diseases. PUBLIC HEALTH REVELANCE: There is compelling evidence that accumulation of a specific protein, the [unreadable]- amyloid peptide, underlies the brain pathology found in Alzheimer's disease, which affects ~5,000,000 people in the US. The proposed study seeks to determine the cellular and molecular basis of [unreadable]-amyloid peptide toxicity. Understanding the toxic mechanism of this protein make be critical for developing therapeutics for Alzheimer's disease.